The present invention relates to integrated circuit packaging and, more particularly, to a method of selectively depositing a plurality of metal layers on a ceramic substrate, particularly multi-layer ceramic (MLC) substrates.
It is well known to use ceramic substrates as supports for mounting semiconductor devices thereon. The present invention is concerned with all ceramic substrates but is of particular importance to MLC substrates. Accordingly, only MLC substrates will be referred to hereafter but it should be understood that the invention has applicability to ceramic substrates in general.
MLC technology for producing substrates for integrated circuit semiconductor package assemblies is well known in the art. Such substrates are produced by preparing a slurry of a suitable particulate ceramic, a resin binder material, a solvent for the resin binder, and generally a plasticizing agent, doctor blading the slurry on a beam and subsequently drying to form thin flexible sheets, commonly termed ceramic green sheets. These sheets are punched to form via holes, and the via holes are filled with a conductive paste and also formed into lines which will ultimately form the internal circuitry. The punched and printed green sheets are assembled into a laminated substrate and then sintered. The resultant substrate is capable of mounting many devices which are interconnected by the internal circuitry. External contact is made by a plurality of I/O pins on the opposite side. The substrate is provided on the top surface with many small pads which are suitable for making solder connections to corresponding device terminals.
Such MLC substrates require a relatively complex metallurgy on the topside to make connections to the integrated circuit devices and provide engineering change pads, and on the bottom to make connection to the I/O pads or other type connections. The complex metallurgy is comprised of several layers of metal which are selectively deposited in a predetermined pattern by additive and/or subtractive photolithographic processes such as those disclosed in, for example, Christensen et al. U.S. Pat. No. 4,526,859, Schmeckenbecher U.S. Pat. No. 4,206,254, IBM Technical Disclosure Bulletin, Vol. 27, No. 6, November 1984, pp. 3341-3342, and IBM Technical Disclosure Bulletin Vol. 26, No. 12, May 1984, p. 6624, all of which are incorporated by reference herein.
Osborne et al. teaches a subtractive process for use in conjunction with thin film magnetic heads. There, a first layer is encapsulated with a protective metal while a second layer is etched.
Notwithstanding the above known processes, there still remains a need for an improved process for selectively depositing a plurality of metallic layers.
Accordingly, it is an object of the invention to have an improved process for selectively depositing a plurality of metallic layers.
It is a further object of the invention to have an improved process for selectively depositing a plurality of metallic layers which is reliable in use.
It is another object of the invention to have an improved process for selectively depositing a plurality of metallic layers which is simpler in operation than known photolithographic processes.
These and other objects of the invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.